This invention relates to dilution control for the combustible charge of an internal combustion engine to optimize engine operation.
The normal method of dilution control in the prior art is the open loop control of an EGR valve in response to sensed engine speed and load variables. Some dilution control systems have also been suggested in which the control is closed loop in response to a combustion pressure parameter. For example, the U.S. Pat. No. 3,977,373, to Sand issued Aug. 31, 1976, discloses that EGR may be varied in response to the value or magnitude of peak combustion pressure in order to maintain it within predetermined limits. U.S. Pat. No. 4,624,229 to Matekunas, issued Nov. 25, 1986, discloses an engine dilution control in which EGR is varied in response to a parameter derived from the final pressure ratio (of combustion pressure to motoring pressure) of an engine combustion event. U.S. Pat. No. 4,531,499 to Eckert et al, issued July 30, 1985, discloses an EGR control responsive to the variability of the amplitude of combustion pressure. However, these systems require a sensor or sensor system which will provide accurate, or at least consistent, values for the amplitude of peak combustion pressure; and such sensors are not necessarily available at a reasonable cost.
A sensor or sensing system for detecting the timing, rather than the amplitude, of peak combustion pressure is easier and less expensive to manufacture. Dilution is also related to the timing of peak combustion pressure, since it affects the rate of combustion. LPP ignition timing controls are known in the prior art. If some part of such an LPP ignition timing control were to indicate the direction to move for optimal dilution control it would be desirable to combine it with a dilution control to form a total engine control system. We have invented such a system.